Turning down requests from recruiters through LinkedIn's InMail request system might block them from ever contacting you again, according to a post on The Next Web. Sogeti USA Corporate Recruiter, Jessica Youngblood, warned job-seekers about the issue in a post on LinkedIn.
At the moment, when you turn down an InMail request from a recruiter, that recruiter will never be able to contact you about any other opportunities ever again. If you are looking for a job, this practice is probably not in your best interest, as you never know if the recruiter you mistakenly block will have the job you've been looking for all along.
Microsoft wants LinkedIn to become the best place to find a job online and become the best professional social network on the web, but this might turn out to stifle LinkedIn's growth if the right people are not getting connected with the right jobs.
LinkedIn has yet to make an official comment on this issue, but it appears that it's gaining traction through Youngblood's post. Maybe LinkedIn will take the appropriate steps to fix this issue to bar any problems with InMail in the future.